The present invention relates to a redialing system for a portable terminal device and, more particularly, to reconnection processing when a channel break (disconnection) occurs due to a radio wave fault during speech communication using a digital channel.
In a portable telephone which is popularly used as a personal communication means and can communicate at an arbitrary location, the received signal intensity largely changes because the distance from the base station changes. In addition, a radio wave attenuates due to the influence of geographical features or buildings to cause multiple propagation and then fading. For this reason, the electric field varies depending on the location. The electric field changes over time in communication during movement. Hence, the channel is assumed to be disconnected.
If speech communication suddenly breaks due to a radio wave fault, and the communication channel is disconnected, a series of cumbersome operations are required: on-hook processing is performed, and then off-hook processing is performed to redial the telephone number of the communication partner. It is preferable to automatically perform redialing to call the partner to continue the communication without requiring the above operations.
As a communication terminal device having such a redialing technique is proposed in Japanese Patent Laid-Open No. 7-87176 (reference 1). According to the communication terminal device of reference 1, a keyboard is operated in calling to read out, from a memory, a telephone number registered in advance and display it on a display device. Calling is performed using the displayed telephone number, and the communication channel is monitored during speech communication with the partner. When a communication channel disconnection is detected, a timer is started to count the communication channel disconnection time. When a predetermined time has been counted, on-hook processing is executed. After this, the telephone number of the communication partner (called party) immediately before the channel disconnection is read out from the memory again and displayed on the display device. Redial processing is executed using the displayed telephone number.
Another telephone device having a redialing technique is proposed in Japanese Patent Laid-Open No. 1-41545 (reference 2). A push-phone and digital telephone for performing a redial operation are disclosed in reference 2. According to the former push-phone, when the called party wants to temporarily disconnect speech communication due to some reason, the called party depresses a registration button and then inputs the telephone number informed from the communication partner (calling party). The input telephone number is written in a dial storage memory and simultaneously displayed on a display device. The registration button is depressed again to complete registration. After this, off-hook processing is performed, and a read button is depressed to redial the telephone number of the communication partner (calling party) immediately before.
According to the latter digital telephone, when a data packet frame having a header field, a data field, and an error check field is received from a digital channel, a calling party address contained in the header field is detected and displayed on a display device. A registration button is depressed during speech communication to write the calling party address displayed on the display device in an address memory. After on-hook, a read button is depressed to read out the calling party address stored in the calling party address memory during speech communication immediately before.
The above-described communication terminal device of reference 1 performs redial processing on the basis of the telephone number read out from the memory in correspondence with the call during speech communication. For this reason, when a channel disconnection occurs during speech communication with a partner whose telephone number is not registered in the memory in advance, redialing cannot be performed.
In addition, since timer processing, telephone number re-read processing, and processing of redisplaying the readout telephone number are required, the redial processing program becomes complex, and the load on the control section comprising a CPU (Central Processing Unit) increases. Furthermore, redial processing corresponding to a channel disconnection during speech communication is possible only for an outgoing call and cannot be performed for an incoming call.
In the analog telephone of reference 2, redial processing is performed on the basis of the telephone number informed from the communication partner (calling party) and stored in the memory. For this reason, this telephone cannot cope with a sudden channel disconnection due to a radio wave fault during speech communication. In addition, the registration button must be operated twice, and the operation of inputting the telephone number of the communication partner, the off-hook operation of redialing the stored telephone number of the communication partner, and the read button operation are required, resulting in cumbersome operations.
The digital telephone of reference 2 performs redial processing on the basis of the calling party address detected from the header field of the received data packet frame and stored and therefore cannot cope with a sudden channel disconnection due to a radio wave fault during speech communication. Although the number of operations by the called party decreases as compared to that of the analog telephone, the registration button operation of storing the calling party address during speech communication is still required.